Gantry cranes are of a type designed to straddle a load, and generally have a pair of side frames connected by a pair of cross rails. The side frames and cross rails are rigidly connected to form a very sturdy unit capable of lifting large loads, and for transporting these loads along the ground. Typically, a pair of lifting winches or the like are mounted on the cross members and may include grappling hooks, load lifting straps, or the like for engaging the load and lifting the same.
Such gantry cranes are commonly used in railroad yards for handling containerized freight or truck trailers, or are used in other storage yards for handling large, bulky loads such as pipe. In construction yards, such cranes find a wide range of use in material distribution, yard maintenance, loading and unloading heavy machinery, and moving fragile equipment. Such cranes are also commonly used for handling large concrete sections such as bridge beams, highway dividers, roof beams, wall sections, large diameter pipe, for launching large boats, and many other applications where the lifting and transport of bulky or difficult to handle items is required.
The gantry cranes in present use typically are provided with one or more wheels at each corner thereof, some or all of which may be steerable and some or all of which may be driven.
The rigid construction of such cranes as heretofore used has been necessary for strength as well as for ease of manipulation and maximum lifting capability. However, the rigidity of such cranes has also been the cause of a significant problem. When such cranes would move along uneven terrain such as would be commonly found in construction yards, railroad yards, or the like, it was not uncommon to have one of the wheels be actually lifted off of the ground at the point where it encountered a low spot. If the wheel which lost ground contact were a steerable wheel or a driven wheel, the crane would lose motive drive and would also lose some steerability. Such cranes were not provided with any type of suspension system which would accomodate uneven terrain.
The present invention overcomes this problem by providing a gantry crane having a strong axis versus weak axis construction which results in a type of "suspension" which enables all of the wheels of the crane to maintain full ground contact over fairly wide variations in terrain. This is achieved by providing a pair of rigid side frames which are pivotally connected at the top rear corners by means of a pivotal connection to a cross beam, and are rigidly connected to a cross beam at the top front corners. The side frames are designed to be substantially rigid, and thus when uneven terrain is encountered, pivotal motion of the rear portion of the frame results in a torsional bending of the front cross beam.
Accordingly, it is a primary object of the present invention to provide a gantry crane which is capable of maintaining full ground contact over uneven terrain.
A further object of this invention is to provide a gantry crane having a strong axis versus weak axis design to provide a type of suspension system.
Still another object of this invention is to provide a gantry crane having an improved operator cab arrangement.
Yet another object of this invention is to provide an improved gantry crane of a type which overcomes the disadvantages of prior art cranes.